1. Field of the Invention
The present invention relates to a process for forming a solid lubricating film on an iron-base alloy substrate such as steel or the like, and a sliding member having a solid lubricating film. In particular, the present invention is applicable to precision sliding component parts for automobiles, electronic appliances or the like. For instance, it is applicable to bearings, mechanical seals, sliding component parts of various pumps or the like therefor.
2. Description of the Related Art
A carbonaceous film has been formed on a substrate of a sliding component part in order to give a lubricating property thereto. The carbonaceous film comprises a carbon-base solid lubricant such as graphite or the like. As for a process for forming the film, a substrate is first coated with an organic polymer, and thereafter an ion irradiation is carried out thereon. Further, another process is proposed in Japanese Unexamined Patent Publication No. 215578/1988, in which an organic material is heated and deposited on a substrate comprising a ceramic, and ions of a predetermined gas element are irradiated thereon, thereby forming a carbonaceous film having a high adhesion property.
In the precision sliding component parts, their sliding portions are required to have a high dimensional accuracy, and further the high dimensional accuracy should be maintained for a long period of time. Accordingly, the film thickness of the carbonaceous film should be made as thin as possible, and the adhesion property thereof to a substrate should be enhanced.
However, the carbonaceous film formed by the above-described process, in which a substrate is first coated with an organic polymer, and thereafter an ion irradiation is carried out thereon, suffers from a large density variation (i.e., contraction) occurring therein. Accordingly, a large strain stress occurs in an interface between the carbonaceous film and the substrate. Therefore, the carbonaceous film has a poorer adhesion property to the substrate, and also has a shorter life.
Further, in the carbonaceous film formed by the process set forth in the Japanese Unexamined Patent Publication No. 215578/1988, the density variation, resulting from the carbonizing organic material, occurs during a stage of an extremely thin film thickness, e.g., during a stage of a single molecule layer or a couple of molecules layer. Therefore, the contraction occurs freely without being restricted. Since the extremely thin film layers are deposited continuously in this process, the carbonaceous film thus formed does not contain the strain stress substantially. Therefore, the carbonaceous film has an enhanced adhesion property to the substrate made of a ceramic, and has a longer life.
However, the carbonaceous film, formed by the process set forth in the Japanese Unexamined Patent Publication No. 215578/1988, comes to have a shorter life when it is slided under a severer sliding condition. Further, in the case where a substrate made of an iron-base alloy is employed in this process, it might be pointed out that the adhesion property of the carbonaceous film to the substrate is expected to improve due to a chemical bond which arises between the substrate made of an iron-base alloy and the carbonaceous film and binds the iron and carbon elements. Although there arises the chemical bond between the iron and carbon elements, it cannot make the carbonaceous film into a solid lubricating film having a longer life under a severer sliding condition.